The present invention relates generally to methods and apparatus for peening components and more particularly to a method and apparatus which prevent damage to corners of components during peening.
Metal components such as those used in gas turbine engines are peened to induce compressive surface stresses. These compressive stresses inhibit crack formation and growth in the component. Because peening inhibits crack formation and growth, peened components generally have longer fatigue lives than unpeened components. However, high intensity peening (e.g., peening to Almen intensities greater than about 0.005 A) sometimes damages corners of components resulting in lower fatigue lives. The corners which are susceptible to damage include corners surrounding holes in components. The damage occurs when the corners are smeared, curled or bent over by the force of peening media hitting the corner during high intensity peening. The bent corners form notches which concentrate stress. Further, the metal at the corners becomes brittle as it is bent. The stress concentrations and brittleness increase the likelihood of crack formation and increase the speed of crack growth in the component.
To determine if corners are damaged by peening, the corners can be inspected following peening. If a damaged corner is found, the component is scrapped or reworked to remove the damaged area. However, corners usually are not inspected for peening damage and peening damage is controlled by controlling the peening process.